[ci] make MiKTeX downloads more reliable (#3124)

* [ci] make MiKTeX downloads more reliable

* switch to Powershell

* remove  extra slash

* fixing stuff

* revert install change

* Update .ci/test_r_package_windows.ps1
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>

.ci/test_r_package_windows.ps1

@@ -12,12 +12,31 @@ function Download-File-With-Retries {
   } while(!$?);
 }
 
+# mirrors that host miktexsetup.zip do so only with explicitly-named
+# files like miktexsetup-2.4.5.zip, so hard-coding a link to an archive as a
+# way to peg to one mirror does not work
+#
+# this function will find the specific version of miktexsetup.zip at a given
+# mirror and download it
+function Download-Miktex-Setup {
+    param(
+        [string]$archive,
+        [string]$destfile
+    )
+    $PageContent = Invoke-WebRequest -Uri $archive -Method Get
+    $SetupExeFile = $PageContent.Links.href | Select-String -Pattern 'miktexsetup.*'
+    $FileToDownload = "${archive}/${SetupExeFile}"
+    Download-File-With-Retries $FileToDownload $destfile
+}
+
 $env:R_WINDOWS_VERSION = "3.6.3"
 $env:R_LIB_PATH = "$env:BUILD_SOURCESDIRECTORY/RLibrary" -replace '[\\]', '/'
 $env:R_LIBS = "$env:R_LIB_PATH"
 $env:PATH = "$env:R_LIB_PATH/Rtools/bin;" + "$env:R_LIB_PATH/R/bin/x64;" + "$env:R_LIB_PATH/miktex/texmfs/install/miktex/bin/x64;" + $env:PATH
 $env:CRAN_MIRROR = "https://cloud.r-project.org/"
-$env:CTAN_MIRROR = "https://ctan.math.illinois.edu/systems/win32/miktex/tm/packages/"
+$env:CTAN_MIRROR = "https://ctan.math.illinois.edu/systems/win32/miktex"
+$env:CTAN_MIKTEX_ARCHIVE = "$env:CTAN_MIRROR/setup/windows-x64/"
+$env:CTAN_PACKAGE_ARCHIVE = "$env:CTAN_MIRROR/tm/packages/"
 
 if ($env:COMPILER -eq "MINGW") {
   $env:CXX = "$env:R_LIB_PATH/Rtools/mingw_64/bin/g++.exe"
@@ -51,14 +70,13 @@ Write-Output "Done installing Rtools"
 # MiKTeX and pandoc can be skipped on non-MINGW builds, since we don't
 # build the package documentation for those
 if ($env:COMPILER -eq "MINGW") {
-    Write-Output "Downloading MiKTeX"
-    Download-File-With-Retries -url "https://miktex.org/download/win/miktexsetup-x64.zip" -destfile "miktexsetup-x64.zip"
+    Download-Miktex-Setup "$env:CTAN_MIKTEX_ARCHIVE" "miktexsetup-x64.zip"
     Add-Type -AssemblyName System.IO.Compression.FileSystem
     [System.IO.Compression.ZipFile]::ExtractToDirectory("miktexsetup-x64.zip", "miktex")
     Write-Output "Setting up MiKTeX"
-    .\miktex\miktexsetup.exe --remote-package-repository="$env:CTAN_MIRROR" --local-package-repository=./miktex/download --package-set=essential --quiet download ; Check-Output $?
+    .\miktex\miktexsetup.exe --remote-package-repository="$env:CTAN_PACKAGE_ARCHIVE" --local-package-repository=./miktex/download --package-set=essential --quiet download ; Check-Output $?
     Write-Output "Installing MiKTeX"
-    .\miktex\download\miktexsetup.exe --remote-package-repository="$env:CTAN_MIRROR" --portable="$env:R_LIB_PATH/miktex" --quiet install ; Check-Output $?
+    .\miktex\download\miktexsetup.exe --remote-package-repository="$env:CTAN_PACKAGE_ARCHIVE" --portable="$env:R_LIB_PATH/miktex" --quiet install ; Check-Output $?
     Write-Output "Done installing MiKTeX"
 
     initexmf --set-config-value [MPM]AutoInstall=1